1. Field of the Invention
The present invention relates to a vane air motor usable as driving means for pneumatic grinders and so forth.
2. Description of the Related Art
Conventionally, a vane air motor has a motor housing having a circular cylindrical inner peripheral surface defining a rotor chamber in the motor housing and a rotor eccentrically and rotatably installed in the motor housing and having vanes. The rotor has an output shaft portion projecting from one end surface of the rotor along the axis of rotation of the rotor. The output shaft portion is rotatably supported by an end wall of the motor housing. The rotor further has a support shaft portion projecting from the other end surface of the rotor in coaxial relation to the output shaft portion. The support shaft portion is rotatably supported by another end wall of the motor housing. The vane air motor further has a governor having a shaft-shaped rotating member coaxially secured to the support shaft portion to rotate together with the support shaft portion. When the shaft-shaped rotating member is rotated at a number of revolutions greater than a predetermined one, the governor limits a compressed air supply flow path supplying compressed air into the rotor chamber to suppress the number of revolutions of the rotor.
The output shaft portion and the support shaft portion are supported by radial bearings provided in the end walls, respectively, of the housing. The radial bearings comprise inner races secured to the output and support shaft portions, respectively, outer races provided radially outward of the respective inner races, and spherical or circular cylindrical rolling members provided between respective combinations of inner and outer races.
The motor housing and the governor are enclosed by a casing of a pneumatic grinder or the like to which the vane air motor is attached, and compressed air to be supplied into the rotor chamber is supplied through a compressed air supply chamber formed around the governor by the casing and through an air supply hole formed in the motor housing (Patent Literature 1 noted below).
Patent Literature: Patent Literature 1: Japanese Patent Application Publication No. 2001-9695
In the vane air motor having the above-described structure, the pressure in the compressed air supply chamber, in which the governor is disposed, is higher than in the rotor chamber in which the rotor is disposed. The rotor chamber and the compressed air supply chamber are divided from each other by the end wall of the motor housing which end wall receives the support shaft portion of the rotor extending therethrough and supports it by means of the radial bearing. Therefore, the above-noted difference in pressure causes grease in the radial bearing to gradually leak into the rotor chamber. Grease entering the rotor chamber adheres to vane end portions near the above-described end wall. Because of its high viscosity, the grease hinders smooth radial movement of the blades relative to the rotor. However, such does not occur at the radial bearing in the other end wall of the motor housing, and no grease adheres to vane end portions near the other end wall. Consequently, each blade is inclined between one end and the other end thereof. For this reason, the distal edge of each vane is pressed against the cylindrical wall surface with a stronger force at one end of the distal edge near the above-described other end wall than the other end of the same, and it is likely that the one end of the distal edge of the vane will become worn or broken.